<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var a = prompt("分数多少？")
        var b = parseInt(a / 10)
        switch (b) {
            case 9 :
            alert('A')
            break;
            case 8 :
            alert('B')
            break;
            case 7 :
            alert('c')
            break;
            case 6 :
            alert('D')
            break;
            default :
            alert('E')
            break;
        }
       

    </script>
</body>
</html>